3,469 research outputs found
Coplanar stripline antenna design for optically detected magnetic resonance on semiconductor quantum dots
We report on the development and testing of a coplanar stripline antenna that
is designed for integration in a magneto-photoluminescence experiment to allow
coherent control of individual electron spins confined in single self-assembled
semiconductor quantum dots. We discuss the design criteria for such a structure
which is multi-functional in the sense that it serves not only as microwave
delivery but also as electrical top gate and shadow mask for the single quantum
dot spectroscopy. We present test measurements on hydrogenated amorphous
silicon, demonstrating electrically detected magnetic resonance using the
in-plane component of the oscillating magnetic field created by the coplanar
stripline antenna necessary due to the particular geometry of the quantum dot
spectroscopy. From reference measurements using a commercial electron spin
resonance setup in combination with finite element calculations simulating the
field distribution in the structure, we obtain an average magnetic field of
~0.2mT at the position where the quantum dots would be integrated into the
device. The corresponding pi-pulse time of ~0.3us fully meets the requirements
set by the high sensitivity optical spin read-out scheme developed for the
quantum dot
Evidence for a very slow X-ray pulsar in 2S0114+650 from RXTE All-Sky Monitor Observations
Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) observations of the
X-ray binary 2S0114+650 show modulations at periods close to both the optically
derived orbital period (11.591 days) and proposed pulse period (~ 2.7 hr). The
pulse period shows frequency and intensity variability during the more than 2
years of ASM observations analyzed. The pulse properties are consistent with
this arising from accretion onto a rotating neutron star and this would be the
slowest such period known. The shape of the orbital light curve shows
modulation over the course of the entire orbit and a comparison is made with
the orbital light curve of Vela X-1. However, the expected phase of eclipse,
based on an extrapolation of the optical ephemeris, does not correspond with
the observed orbital minimum. The orbital period derived from the ASM light
curve is also slightly longer than the optical period.Comment: To be published in the Astrophysical Journal, 1999, volume 511. 9
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Electrical control of the exciton-biexciton splitting in a single self-assembled InGaAs quantum dots
We report on single InGaAs quantum dots embedded in a lateral electric field
device. By applying a voltage we tune the neutral exciton transition into
resonance with the biexciton using the quantum confined Stark effect. The
results are compared to theoretical calculations of the relative energies of
exciton and biexciton. Cascaded decay from the manifold of single
exciton-biexciton states has been predicted to be a new concept to generate
entangled photon pairs on demand without the need to suppress the fine
structures splitting of the neutral exciton
Molecular Mechanics Simulations and Improved Tight-binding Hamiltonians for Artificial Light Harvesting Systems: Predicting Geometric Distributions, Disorder, and Spectroscopy of Chromophores in a Protein Environment
We present molecular mechanics {and spectroscopic} calculations on prototype
artificial light harvesting systems consisting of chromophores attached to a
tobacco mosaic virus (TMV) protein scaffold. These systems have been
synthesized and characterized spectroscopically, but information about the
microscopic configurations and geometry of these TMV-templated chromophore
assemblies is largely unknown. We use a Monte Carlo conformational search
algorithm to determine the preferred positions and orientations of two
chromophores, Coumarin 343 together with its linker, and Oregon Green 488, when
these are attached at two different sites (104 and 123) on the TMV protein. The
resulting geometric information shows that the extent of disorder and
aggregation properties, and therefore the optical properties of the
TMV-templated chromophore assembly, are highly dependent on the choice of
chromophores and protein site to which they are bound. We used the results of
the conformational search as geometric parameters together with an improved
tight-binding Hamiltonian to simulate the linear absorption spectra and compare
with experimental spectral measurements. The ideal dipole approximation to the
Hamiltonian is not valid since the distance between chromophores can be very
small. We found that using the geometries from the conformational search is
necessary to reproduce the features of the experimental spectral peaks
Concorde Noise-Induced Building Vibrations, Montgomery County, Maryland
A series of studies are reported to assess the noise induced building vibrations associated with Concorde operations. The levels of induced vibration and associated indoor/outdoor noise levels resulting from aircraft and nonaircraft events in selected homes, historic and other buildings near Dulles International Airport were recorded. The building response resulting from aircraft operations was found to be directly proportional to the overall sound pressure level and approximately independent of the aircraft type. The noise levels and, consequently, the response levels were observed to be higher for the Concorde operations than for the CTOL operations. Furthermore, the vibration could be closely reproduced by playing aircraft noise through a loudspeaker system located near the vibration measurement location. Nonaircraft events such as door closing were again observed to result in higher response levels than those induced by aircraft
Solutions of the sDiff(2)Toda equation with SU(2) Symmetry
We present the general solution to the Plebanski equation for an H-space that
admits Killing vectors for an entire SU(2) of symmetries, which is therefore
also the general solution of the sDiff(2)Toda equation that allows these
symmetries. Desiring these solutions as a bridge toward the future for yet more
general solutions of the sDiff(2)Toda equation, we generalize the earlier work
of Olivier, on the Atiyah-Hitchin metric, and re-formulate work of Babich and
Korotkin, and Tod, on the Bianchi IX approach to a metric with an SU(2) of
symmetries. We also give careful delineations of the conformal transformations
required to ensure that a metric of Bianchi IX type has zero Ricci tensor, so
that it is a self-dual, vacuum solution of the complex-valued version of
Einstein's equations, as appropriate for the original Plebanski equation.Comment: 27 page
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